The present invention relates to a magnetic recording and reproducing apparatus such as a video tape recorder which permits high speed transport of a magnetic tape bidirectionally in forward and reverse directions.
Whenever a magnetic tape is loaded or unloaded the tape position is shifted a little bit so that the tape may slacken or jump in the recording or playback operation. In the past, in order to prevent such phenomenon, a break force is applied to a take-up reel mount in the loading or unloading period and the tape is unwound in the loading operation or wound in the unloading operation by a supply reel mount. On the other hand, a recent trend of a video tape recorder (VTR) requires high speed tape transport in a reverse direction such as reverse playback or review. In such a case, if the tape unwound from the reel mount is driven by the pinch by a pinch roller and a capstan, the tape may be unwound too much or too little at the capstan position unless a predetermined amount of brake force is imparted to the supply reel mount and as a result the tape may be damaged. Accordingly, it is essential to apply the brake force to the supply reel mount in the reverse tape transport, that is, the take-up reel in the forward tape transport. In the past, in order to impart the brake force to the take-up reel mount (in the forward tape transport) in the reverse tape transport operation as well as in the tape loading and unloading operations, a clutch mechanism has been used. In a remote control equipment, a specially designed electromagnet has been used as a power source for driving the clutch.
On the other hand, a tape take-up mechanism at a reel shaft in the forward tape transport usually uses engagement and disengagement of an idler through a friction torque limiter mechanism. When it is desired to transport the tape in the reverse direction in such an equipment, it is essential to release the transmission drive of the idler mechanism to disable it because the tape would otherwise be transported excessively since the tape drive speed at the reel mount is higher than the tape drive speed at the capstan. In the past, in order to transport the tape in the reverse direction in this type of mechanism, a special electromagnet has been provided to release the idler. A braking mechanism for the supply reel mount in the forward tape transport usually comprises a conventional tension servo mechanism which includes a combination of an arm having a tension pin and a band brake. In such a system, however, the brake force acts as a load to the take-up reel in the reverse tape transport, and in a high speed reverse tape transport the arm having the tension pin hunts to create variation in the tape tension in the tape path, resulting in the disturbance in a playback image. Accordingly, it is desirable to retract the tension pin away from the tape path. For this reason, in the past, the exclusive electromagnets actuated in the reverse tape transport have been used. As a result, the equipment has been very expensive.
A magnetic recording and reproducing apparatus in which the take-up and supply reel mounts are independently and directly driver by respective motors has been known. In this type of apparatus, a tension servo mechanism including a light source and a light sensor instead of the band brake is used. The brake forces to the reel mounts are applied by applying back voltages to the respective motors. Since such apparatus uses a plurality of motors and complex control, the apparatus is expensive.